Sleep Basics

 

Sleep is a physical and mental resting state in which a person becomes relatively inactive and unaware of the environment.

Normal sleep is characterized by a decrease in body temperature, blood pressure, breathing rate and most other body functions but the brain remains active.

Wakefulness is a state of awareness in which the individual is conscious of his/her surrounding environment and is able to react with it.

Sleep Cycle

Sleep CycleSleep is characterized by two distinct states, non-REM sleep and REM sleep that alternate in 90 to 110-minute cycles.A normal sleep pattern has 4-5 cycles throughout the night.

Sleep Cycle

The stages of sleep are determined with a polysomnogram (PSG). The PSG records vital signs and physiology during sleep including:

  • Electro-encephalogram (EEG)
  • Electro-myograph (EMG)
  • Electro-oculograph (EOG)
  • Respiratory airflow
  • Blood oxygen saturation
  • Pulse rate
  • Heart rate
  • Body position
  • Respiratory effort
  • Cardiac arhythmias

Non-REM sleep consists of four stages that range from light dozing to deep sleep. Approximately 75% of night’s sleep is spent in non-REM sleep.

N1 (Stage 1) -Sleep is a transition period from wakefulness to sleep. It is characterized by slow rolling eye movements. The “dozing” stage.Approximately 5% of the the total night's sleep is spent in Stage 1.

N2 (Stage 2) - Sleep is characterized by a lack of eye movements. Brain waves become larger.
Defined on PSG with sleep spindles and K-complexes. Approximately 45% of the total night's sleep time is spent in Stage 2 of non-REM sleep. This stage is often considered the official onset of consolidated sleep. Eye movements stop and brain waves become larger. Stage 2 Sleep is graphically defined with two distinct brain wave forms called sleep spindles and K-complexes. A sleep spindle is a pattern of EEG waves, consisting of a burst of 11 to 15 hertz waves that last for .5 to 1.5 seconds. A K-complex is high voltage EEG activity that consists of a sharp downward component followed by a slower upward component and lasts more than .5 second.

In N3 (Stage 3 & 4) sleep, an individual becomes difficult to arouse. On the PSG, large and slow delta waves appear. Approximately 12% of the total night's sleep time is spent in N3 sleep. Sleep is characterized by very deep sleep. When awakened, person feels groggy and disoriented.PSG shows delta waves almost exclusively. Approximately 13% of the total night's sleep time is spent in Stage 4 of non-REM sleep.

R (REM Sleep)

Most dreaming takes place during R sleep. R sleep makes up about 20 – 25% of the sleep cycle in normal adults. R sleep is characterized by:

  • Eyelid fluttering
  • Rapid eye movement
  • Muscle paralysis
  • Irregular breathing
  • Decrease in body temperature
  • Changes in heart rate and blood pressure